This invention relates to a composition and process for preparing an aqueous emulsion composition of a fluorochemical copolymer for imparting oil and water repellency to textiles, particularly to cotton or cotton blends, wherein the resulting textile has effective and highly durable initial and post-washing oil and water repellency.
For many years the public has been accustomed to purchasing fabrics or garments prepared from natural cellulosic fibers such as cotton or its blends to which various sizing, repellency-enhancing and/or softening additives have been added to provide improved characteristics. However, these additives may also add undesirable characteristics to the fibers. As a result, it has become the practice to add one or more complementary materials which compensate for the imperfections of the various additives.
For example, crease-resistant resins added to fabrics consisting wholly or partially of cellulosic fibers provide enhanced appearance and minimize ironing, but at the same time the fabric is found to be more receptive to stains, particularly to oily stains. Release of these stains during cleaning, especially laundering, is found to be extremely difficult. This tendency can be alleviated by supplementing the fabric finish with a polymer containing fluoroaliphatic radicals. This confers a high degree of oil and water repellency to the fabric, and reduces the tendency to accept stains. A further improvement can be made by adding to the fluoropolymer an ingredient containing a hydroxyl group or other hydrophilic group to aid in releasing soil during laundering.
A fabric treated with resins also may have a harsher feel. Fabric softness can be improved by adding to the fluoropolymer an ingredient containing fatty alkyl groups.
The prior art discloses numerous specific polymers intended for application to textiles to bestow oil and water repellency properties. Such polymers are generally made from monomers which contain pendant perfluoroalkyl groups of three or more carbon atoms which provide the desired repellencies. These monomers are then generally copolymerized with other monomers to confer additional favorable properties to the textile fabrics. These polymers are generally marketed as aqueous emulsions for easy application to the fabric. The fabric-treating composition may also include other additives in addition to those copolymerized with the fluoropolymer. In particular, various compounds such as blocked isocyanates are frequently added after polymerization to promote durability of a desired property such as repellency. In such applications, the blocking agent is removed from the isocyanate under the thermal conditions used when curing the treated fabric, allowing the isocyanate group to interact with the fabric and improve the desired durability.
In one class of such compounds found to be useful for treating cotton or cotton blends, the perfluoroalkyl groups are connected to polyurethane groups as monomers. However, such urethanes and their isocyanate intermediates are costly and potentially hazardous to manufacture.
In a second class of fluoropolymers useful for treating cotton and cotton blends, the perfluoroalkyl groups are connected to (meth)acrylate groups. By xe2x80x9c(meth)acrylatexe2x80x9d is meant methacrylate, acrylate, or a combination of these groups. These fluoropolymers can be copolymerized with other monomers, such as non-fluorine-containing (meth)acrylate compounds containing a long-chain fatty alkyl group and/or a hydrophilic group. These products have the advantage that they do not involve costly and potentially hazardous isocyanate/urethane chemical manufacturing steps (except indirectly, for any blocked isocyanates added).
A fluorochemical copolymer composition for imparting oil and water repellency to fabrics which is more effective than existing urethane or (meth)acrylate fluoropolymers would have widespread applications, in particular wherein the resulting textile has effective and highly durable initial and post-washing oil and water repellency. The present invention provides such fluorochemical copolymer compositions.
The present invention comprises an oil- and water-repellent aqueous emulsion prepared by:
1) forming a monomer mixture comprising by weight:
(a) 70-90% polymer chain units derived from a mixture of monomers of the formula:
Rfxe2x80x94Qxe2x80x94Axe2x80x94C(O)xe2x80x94C(R)xe2x95x90CH2
xe2x80x83wherein
Rf is a straight or branched-chain perfluoroalkyl group containing from 2 to about 20 carbon atoms,
R is H or CH3,
A is O, S, or N(Rxe2x80x2),
Q is alkylene of 1 to 15 carbon atoms, hydroxyalkylene of 3 to 15 carbon atoms, xe2x80x94(CnH2n)(OCqH2q)mxe2x80x94, xe2x80x94SO2xe2x80x94NRxe2x80x2(CnH2n)xe2x80x94, or xe2x80x94CONRxe2x80x2(CnH2n)xe2x80x94, wherein Rxe2x80x2 is H or alkyl of 1 to about 4 carbon atoms, n is 1 to about 15, q is 2 to about 4, and m is 1 to about 15;
(b) 5-25% monomer chain units derived from a long-chain alkyl (meth)acrylate of the formula:
Rxe2x80x3xe2x80x94Oxe2x80x94C(O)xe2x80x94C(R)xe2x95x90CH2
xe2x80x83wherein Rxe2x80x3 is an alkyl group of about 12 to about 24 carbons and R is H or CH3;
(c) 0.1-2.5% monomer chain units derived from compounds of the formulas:
HOxe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94C(O)xe2x80x94C(R)xe2x95x90CH2
xe2x80x83or
HOxe2x80x94CH2xe2x80x94N(H)xe2x80x94C(O)xe2x80x94C(R)xe2x95x90CH2,
xe2x80x83wherein R is H or CH3;
2) polymerizing the mixture of monomers (a), (b) and (c) in an organic solvent using a free radical initiator as catalyst;
3) adding, in an organic solvent or alone, 10-90% of a blocked aromatic isocyanate (d) relative to the weight of fluoropolymer, with both weights on a solvent-free basis;
4) adding the mixed fluoropolymer-isocyanate solvent solution to water under conditions so as to create an aqueous dispersion of the fluoropolymer-isocyanate mixture; and,
5) removing most or all of the organic solvent from the aqueous dispersion of the fluoropolymer-isocyanate mixture.
The present invention further comprises a process for preparing an oil- and water-repellent aqueous emulsion comprising steps (1) through (5) as recited above.
The present invention further comprises a method of treating fabrics or fabric blends to impart oil- and water-repellency comprising application to the surface of the fabric or fabric blend of an effective amount of the inventive aqueous emulsion as described above.
The present invention still further comprises a fabric or fabric blendwhich has been treated according to the method of the present invention as described above.
In the present description trademarks are indicated by capitalization.
The present invention comprises a process for preparing an aqueous emulsion, and the resulting emulsion, useful for imparting oil- and water-repellency with high washing durability to fabrics or fabric blends, particularly to cotton fabrics or blends. By xe2x80x9cfabricsxe2x80x9d is meant natural or synthetic fabrics composed of fibers of cotton, rayon, silk, wool, hemp, polyester, spandex (including LYCRA), polypropylene, polyolefins, nylon, aramids, and poly(trimethylene terephthalate). By xe2x80x9cfabric blendsxe2x80x9d is meant fabrics made of two or more types of fibers. Typically these blends are a combination of a natural fiber and a synthetic fiber, but can also include a blend of two natural fibers or two synthetic fibers. Superior oil- and water-repellency properties can be imparted to fabrics or fabric blends by the addition of certain fluorochemical copolymers. These can be applied to the fabric in the form of an emulsion or dispersion in water or other solvent either before, after or during the application of other fabric treatment chemicals.
The inventive, highly efficient copolymers useful for this purpose are characterized in that they are made by forming a monomer mixture of (a) a perfluoroalkyl compound, (b) a long-chain alkyl (meth)acrylate and (c) hydroxyethyl methacrylate or hydroxyethyl (meth)acrylamide, polymerizing the monomer mixture in an organic solvent, adding a blocked aromatic isocyanate (d) to the fluoropolymer solution, adding a water/surfactant mixture in such a way as to form an aqueous dispersion of the fluoropolymer-isocyanate mixture, and removing most or all of the organic solvent from the resulting aqueous dispersion.
In forming the above monomer mixture, the perfluoroalkyl compound (a) has the formula:
Rfxe2x80x94Qxe2x80x94Axe2x80x94C(O)xe2x80x94C(R)xe2x95x90CH2
wherein
Rf is a straight or branched-chain perfluoroalkyl group containing from 2 to about 20 carbon atoms,
R is H or CH3,
A is O, S, or N(Rxe2x80x2),
Q is alkylene of 1 to about 15 carbon atoms, hydroxyalkylene of 3 to about 15 carbon atoms, xe2x80x94(CnH2n)(OCqH2q)mxe2x80x94, xe2x80x94SO2xe2x80x94NRxe2x80x2(CnH2n)xe2x80x94, or xe2x80x94CONRxe2x80x2(CnH2n)xe2x80x94, Rxe2x80x2 is H or alkyl of 1 to about 4 carbon atoms, n is 1 to about 15, q is 2 to about 4, and m is 1 to about 15.
Preferably monomer (a) is a perfluoroalkylethyl (meth)acrylate. More preferably the perfluoroalkyl carbon chain length distribution by weight is about 50% of 8-carbon, about 29% of of 10-carbon, about 11% of 12-carbon, and with smaller percentages of 6-carbon, 14-carbon and longer chain lengths. This composition is available as ZONYL TA-N from E.I. du Pont de Nemours and Company of Wilmington, Del.
The proportion of monomer (a) is at least about 70% relative to the total weight of copolymer. If it is present in lower amounts, the oil repellency drops off to an undesirable level. The proportion of monomer (a) is less than about 90%. If it is present in higher amounts, repellency will also be adversely affected, and the cost will be prohibitively higher.
The long-chain alkyl methacrylate (b) has the formula:
Rxe2x80x3xe2x80x94Oxe2x80x94C(O)xe2x80x94C(R)xe2x95x90CH2
wherein Rxe2x80x3 is an alkyl group of about 12 to about 24 carbons and R is H or CH3. The long-chain alkyl (meth)acrylate is added so as to constitute 5-25% of the monomer chain units on a weight basis. If the percentage is below 5%, the fluorine efficiency of the copolymer will be reduced, resulting in higher cost. If the percentage is above 25%, water and oil repellency will be inadequate. Preferably the long-chain alkyl (meth)acrylate (b) is stearyl methacrylate. These monomers can be readily prepared by conventional methods known in the art.
The hydroxyethyl methacrylate or (meth)acrylamide (c) has the formula:
HOxe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94C(O)xe2x80x94C(CH3)xe2x95x90CH2
or
HOxe2x80x94CH2xe2x80x94N(H)xe2x80x94C(O)xe2x80x94C(R)xe2x95x90CH2 ,
wherein R is H or CH3.
This compound is added so as to constitute 0.1-2.5% of the monomer chain units on a weight basis. If the percentage is below 0.1%, durability to washing will be inadequate. If the percentage is above 2.5%, the oil and water repellency will be adversely affected. These ingredients are available by purchase from Rohm and Haas Company, Philadelphia, Pa.
The above mixture of monomers (a), (b) and (c) is then polymerized in an organic solvent such as methyl isobutyl ketone, acetone, ethyl acetate, isopropanol, or other ketones, esters and alcohols. By xe2x80x9corganic solventxe2x80x9d is meant an organic compound in which the above monomer mixture is soluble to an amount of at least 10% by weight within the range of temperatures for the polymerization reaction. The solvent may also contain a slight amount of water, providing that it does not interfere with the required solubility.
The polymerization is conveniently initiated by azo initiators such as 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile). This and other suitable initiators are sold by E.I. du Pont de Nemours and Company, Wilmington, Del., under the name of VAZO 67, 52 and 64. Optionally, a chain transfer agent such as dodecyl mercaptan is also used in the polymerization.
In widely used processes for such fluoropolymer repellents, such polymerizations are carried out in aqueous emulsions, since the product will be sold and used in that form. Generally, the product obtained by emulsion polymerization has been regarded as superior to the product obtained by solvent polymerization in performance and ease of production. Unexpectedly it has been found that this is not true for the composition of this invention, in which a blocked isocyanate is added to the fluoropolymer. For maximum post-washing oil and water repellency of the treated fabric, we have found that it is important that the fluoropolymer be present in an organic solvent rather than an aqueous emulsion when the blocked isocyanate is added.
While not wishing to be bound by theory, it is believed that a more intimate mixing of the fluoropolymer and blocked isocyanate at the molecular level may occur because both components are soluble in the organic solvent or solvents chosen, and that this more intimate mixing leads to a more effective fabric treating composition. In contrast, when the fluoropolymer is made by emulsion polymerization, and the blocked isocyanate is then added, even the most intensive mixing may not lead to complete uniformity at the molecular level.
A blocked aromatic isocyanate (d) is then added to the solvent solution of the fluoropolymer formed by polymerization of monomers (a), (b) and (c). By xe2x80x9caromatic isocyanatexe2x80x9d is meant isocyanate compounds with at least one aromatic group, such as materials based on toluene diisocyanate, diphenylmethane 4,4xe2x80x2 diisocyanate, diphenylmethane 2,4xe2x80x2 diisocyanate, polymethylenepolyphenyl isocyanate, 4,4xe2x80x2 methylene bisphenol isocyanate, and derivatives thereof. The amount of blocked isocyanate is at least 10% of the weight of the total fluoropolymer (with both on a solvent-free basis). This amount is required for adequate durability of the post-washing repellency of the treated fabric or fabric blend. If the amount of blocked isocyanate is greater than 90%, there will be too small an amount of fluoropolymer to provide satisfactory initial repellency, and it may result in an overly harsh fabric feel.
Typically, the blocked isocyanate is made by reacting the chosen isocyanate or isocyanate derivative with the blocking agent in an aprotic organic solvent solution, making it convenient to add it in solution form to the fluoropolymer solution. Preferably the same organic solvent is used as for the fluoropolymerization reaction, as long as the organic solvent for the blocking process is aprotic, thus simplifying solvent recovery operations. However, it is also acceptable to isolate the blocked isocyanate from solution or otherwise prepare an isolated blocked isocyanate by methods known to those skilled in the art and add the undissolved isocyanate to the fluoropolymer solution.
xe2x80x9cBlocked isocyanatexe2x80x9d is used herein to mean the reaction products of an isocyanate and a blocking agent, wherein the blocking agent is removable from the isocyanate under the thermal conditions employed upon curing a fabric treated with a compound containing the blocked isocyanate group. These are frequently used to add durability to certain properties of treated fabrics. Conventional blocking agents include aryl alcohols, alkanone oximes, aryl thioles, organic active hydrogen compounds, sodium bisulfite and hydroxylamine. Preferred blocking agents are alkanone oximes (ketoximes), which can be de-blocked at a relatively low temperature such as used during a typical fabric curing process. Particularly preferred is butanone oxime.
Suitable isocyanates A(CNO)x for preparation of the blocked isocyanate are those wherein A is an aromatic compound, and x is 1, 2, 3 or 4. These include isocyanates or derivatives such as toluene diisocyanate, polymethylenepolyphenyl isocyanate, and 4,4xe2x80x2 methylene bisphenol isocyanate, and include those aromatic isocyanates sold commercially for this purpose. Typical commercial products include products such as the adduct of toluene diisocyanate and trimethylolpropane (1,1.1 trihydroxymethyl propane (DESMODUR CB-75; available from Bayer Corp., Pittsburg, Pa.), aromatic isocyanates based on the polymethylenepolyphenylene ester of isocyanic acid, such as MONDUR MR-100 (available from Bayer Corp.), and aromatic isocyanates based on polymethylenepolyphenyl isocyanate containing 4,4xe2x80x2 methylene bisphenol isocyanate (available from Dow Chemical Co., Midland, Mich.). Also available commercially are already-combined blocked aromatic isocyanates such as HYDROPHOBOL XAN and HYDROPHOBOL DL, (available from Ciba Specialty Chemicals, Langweid, Germany). Suitability for use in this invention may easily be determined by one skilled in the art.
The blocked isocyanate and fluoropolymer are then mixed as a solution. This is done most readily if the separately-made blocked isocyanate and fluoropolymer use the same organic solvent, and their solutions are simply mixed together. The mixing may be done at any convenient temperature below the point where the blocking agent starts to volatilize or undergo significant deblocking.
It is important that the blocked isocyanate and fluoropolymer be combined in an organic solvent or solvents. Samples where the blocked isocyanate and fluoropolymer are dispersed in water separately and then combined show inferior initial and post-washing repellencies.
The mixed isocyanate-fluoropolymer solvent solution is then added to water and an effective amount of surfactant or surfactants with sufficient agitation so as to create an aqueous dispersion of fluoropolymer and isocyanate. The various methods for carrying out this step are well known to those familiar with the art. Preferred surfactants are cationic or nonionic. Examples of suitable cationic dispersants are quaternary ammonium- and pyridinium salts such as stearyldimethylbenzylammonium chloride. An example of a suitable nonionic surfactant is MERPOL SE, available from Stepan Co., Northfield, Ill.
Next the solvent is removed from the aqueous dispersion of fluoropolymer and blocked isocyanate by a means such as distillation or thin layer evaporation. If desired the solvent is returned to the process as recycled material. The solvent is removed, for example, at elevated temperature (40-90xc2x0 C.) in vacuo. In principle it is possible to leave a fairly large proportion of solvent present in the dispersions. However, for reasons of work safety and industrial hygiene the solvent is preferentially distilled off to such an extent that the flash points of the dispersions are above 100xc2x0 C. After removal of the solvent the aqueous dispersions are stable.
The present invention further comprises a method of treating fabrics or fabric blends comprising application to the surface of the fabric or fabric blend of an effective amount of the fluoropolymer-isocyanate aqueous emulsion. The emulsion is applied to the fabric or fabric blend to be treated, either alone or in a mixture with other textile treatment agents or finishes. The emulsion is applied in an amount to provide a fluorine content on the fabric of from about 0.5% to about 5.0% by weight. The emulsion is generally applied to textile fabrics by spraying, dipping, padding, or other well-known methods. After excess liquid has been removed, for example by squeeze rolls, the treated fabric is dried and then cured by heating, for example, at from 100xc2x0 to 1900xc2x0 C., for at least 30 seconds, typically 60-180 seconds. Such curing enhances durability of the repellent finish. While these curing conditions are typical, some commercial apparatus may operate outside these ranges because of its specific design features.
The present invention further comprises a fabric or fabric blend which has been treated to impart oil- and water-repellent properties thereto by application of an effective amount of a copolymer-isocyanate mixture as described above. The treated fabric has a fluorine content of from about 0.5% to about 5.0% by weight. The treated fabric has superior oil- and water-repellencies, especially in terms of durability after washing.
The fluoropolymers and method of the present invention are useful to create an oil- and water-repellency durability that is highly durable even after multiple launderings. The improvement in durability is especially evident for fabrics treated with permanent press resins. The treated fabrics and fabric blends of the present invention are useful for a variety of applications such as textiles, clothing, furnishings and the like. The fluoropolymer ingredients of the present invention are advantageous in that they are safer to manufacture than the urethane type fluoropolymer, and are made at lower materials cost than urethane-based fluoropolymers, in part because the gas/liquid reactions required for manufacturing phosgene and intermediate isocyanate fluorochemicals are eliminated. The invented compositions thus provide a higher degree of durable oil and water repellency to treated fabrics at lower cost. In addition, the treated fabrics of this invention can regain repellency properties after laundering by simply tumble drying or brief pressing.
The above dispersions were tested for repellency performance by first padding on tan 100% cotton fabric, using a defined amount of fluorochemical treatment agent along with PERMAFRESH MSC, a permanent press resin available from Sequa Chemicals Inc, Chester, S.C., and cured at 330xc2x0 C. for two minutes. The treated fabrics were repeatedly laundered and dried by the standardized procedure described below before testing for oil and water repellency.
Laundering Procedure
The fabric samples were laundered according to the U.S. Home Laundering Method outlined in the TEFLON Global Specifications and Quality Control Tests information packet. Fabric samples are loaded into a KENMORE automatic washer with a ballast load to give a total dry load of 4 lb. A commercial detergent is added (AATCC 1993 Standard Reference Detergent WOB) and the washer is filled to a high water level with warm water (105xc2x0 F.)(41xc2x0 C.). The samples and ballast are washed a designated number of times (5HW=5 washes, 10HW=10 washes, etc.) using a 12-minute normal wash cycle followed by rinse and spin cycles. The samples are not dried between wash cycles.
After washing is complete, the wet fabric samples and ballast are transferred to a KENMORE automatic dryer and dried for 45 minutes at the high/cotton setting to achieve a vent temperature of 155-160xc2x0 F. (68-71xc2x0 C.).
Water Repellency
The water repellency of a treated fabric was measured by determining the resistance of the fabric by wetting with various aqueous liquids. The test is outlined in the TEFLON Global Specifications and Quality Control Test information packet, available from E.I. du Pont de Nemours and Company. Drops of water/alcohol mixtures of various surface tensions were placed on the treated fabric and the extent of surface wetting determined visually. The ratings correspond to the numbers given to the water/alcohol mixtures as shown in the table below. The numbers are assigned such that the higher the rating, the better the resistance of the fabric to more penetrating water/alcohol blends. This test of water/alcohol repellency also provides a rough index of the aqueous stain resistance of the fabric. The test water/alcohol mixtures and their numbers are shown in the following table.
Spray Rating
The spray rating of a fabric is a value showing the repellency of the fabric to a water spray. The treated fabric samples were tested for their spray rating using AATCC standard Test Method No. 22 of the American Association of Textile Chemists and Colorists. In this test, 250 mL of water at 27xc2x0 C. is poured on a fabric sample stretched on a 6 inch (15.2 cm) diameter metal hoop. The water is discharged from a funnel suspended 6 inches (15.2 cm) above the fabric sample. After removal of excess water, the fabric is visually scored by reference to published standards. A rating of 100 denotes no water penetration or surface adhesion; a rating of 90 denotes slight random sticking or wetting; lower values denote greater wetting.
Oil Repellency
The treated fabric samples were tested for oil repellency by a modification of AATCC standard Test Method No. 118, conducted as follows. A fabric sample, treated with an aqueous dispersion of polymer as previously described, is conditioned for a minimum of 2 hours at 23xc2x0 C. at 20 % relative humidity and 65xc2x0 C. at 10% relative humidity. A series of organic liquids, identified below in Table I, are then applied dropwise to the fabric samples. Beginning with the lowest numbered test liquid (Repellency Rating No. 1), one drop (approximately 5 mm in diameter or 0.05 mL volume) is placed on each of three locations at least 5 mm apart. The drops are observed for 30 seconds. If, at of the three drops are still spherical in shape with no wicking around the drops, three drops of the next highest numbered liquid are placed on adjacent sites and similarly observed for 30 seconds. The procedure is continued until one of the test liquids results in two of the three drops failing to remain spherical to hemispherical, or wetting or wicking occurs.
The oil repellency rating of the fabric is the highest numbered test liquid for which two of the three drops remained spherical to hemispherical, with no wicking for 30 seconds. In general, treated fabrics with a rating of 5 or more are considered good to excellent; fabrics having a rating of one or greater can be used in certain applications.